Oh, Weng Chin
(2017)
Micronutrient losses during renal replacement therapy for acute kidney injury.
DM thesis, University of Nottingham.
Abstract
Malnutrition is common in acute kidney injury (AKI) patients, particularly on the ICU, where they often receive renal replacement therapy (RRT). RRT may exacerbate loss of water-soluble micronutrients (e.g. trace elements, amino acids and B-vitamins). No clinical study has quantified these losses and contrasted between types of RRT that use different methods to remove solutes i.e. by diffusion (intermittent haemodialysis, IHD) by convection (continuous veno-venous haemofiltration, CVVH) or by a combination of both (sustained low-efficiency diafiltration, SLEDf).
Using a prospective, observational design patients (n=24 per modality) were consented before their first treatment session. Blood and RRT effluent (dialysate or filtrate) were sampled at baseline (pre-RRT), mid and end-RRT. Amino acids were measured by HPLC, trace elements by ICP-MS and B-vitamins (B1, B3, B6, B9, B12) by LC-MS. Plasma concentrations were corrected for dialysis dose using the urea reduction ratio (for IHD & SLEDf, but not CVVH). Micronutrient losses (mass-corrected) were calculated as concentration × RRT effluent volume, corrected for plasma concentration and RRT dose (i.e. solute removal index). Data were analysed by restricted maximum likelihood estimating equations (Genstat v16, VSNi Ltd, UK).
Patients receiving CVVH had significantly higher plasma amino acids, but not plasma trace elements, at baseline (amino acids: CVVH, 3762 ± 357; IHD, 2039 ± 337; SLEDf, 2505 ± 423 µmol/L; trace elements: IHD, 4156 ± 465; SLEDf 3732 ± 521; CVVH 3982 ± 465 µg/L). At RRT end, plasma amino acids and trace elements had significantly reduced (429 ± 223 µmol/L; 600 ± 400 µg/L, respectively). No trace element was lost to a greater extent between types of RRT, but many (>10) individual amino acids declined to a much greater extent with SLEDf vs. HD or CVVH (e.g. effect size for lysine was -64 ± 23 µmol/L). Two significant sources of micronutrient loss were noted: to effluent and through dialyser adsorption. The latter contributed <1g amino acids but in effluent recorded losses of up to 25g were noted with CVVH (5-10g for IHD and SLEDf, respectively). Effluent losses of trace elements varied significantly, but in all cases were greater for CVVH (e.g. effect size for copper was +850 ± 475 µg vs. HD or SLED-F). B-vitamins were not detectable in effluent.
Significant loss of micronutrients during RRT, particularly for patients in ICU, is a possible aggravating factor for patients known to be at high risk of malnutrition. The type of RRT used influences the pattern of loss but not consistently for all nutrients. Adsorption of amino acids to dialysers adds a small, but cumulative loss that may become important if further treatment sessions are indicated.
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